Auxiliary power supply for switch-mode power supplies

ABSTRACT

A combined voltage regulator and snubber circuit generally has a voltage regulator device in parallel with the energy storage element of the snubber circuit operatively connectable in series with a leakage inductance current path; the leakage inductance being part of a magnetic component utilized in a switch-mode power supply having an input voltage source, controllable semiconductor switches, freewheeling semiconductor switches, feedback controller, reactive energy storage components and a load; the voltage regulator generally providing constant or variable voltage to the gate driver of the controllable semiconductor and/or feedback controller.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Non-Provisional applicationSer. No. 15/387,789, filed Dec. 22, 2016, all of which is incorporatedby reference herein in its entirety.

TECHNICAL FIELD

Example embodiments generally relate to the field of switch-mode powersupplies, and more particularly to the field of high-efficiencyhigh-side auxiliary power supplies and leakage inductance energyrecycling.

BACKGROUND

Switch-mode power supplies (SMPS) are power management components inmodern electronic devices that provide, among other things,well-regulated power to electronic loads while minimizing the powerprocessing losses and maximizing the SMPS power density. Some solutionsprovide improved SMPS switching frequency and semiconductortechnologies. These solutions may suffer from diminishing returns and/orprohibitive cost.

While the series-input architectures enable power density and powerprocessing efficiency, these architectures usually require at least onehigh-side gate-driver and an associated auxiliary power supply. Theseadditional circuits contribute to an increased bill-of-material,component count, quiescent current and potentially decreasedreliability.

Additional difficulties may be appreciated in view of the DetailedDescription of Example Embodiments, herein below.

SUMMARY

In accordance with an example embodiment, there is provided a normallyon switch and associated turn-off circuit for further reducing theauxiliary power supply losses, having automatic turn-off capabilitiesduring light-to-heavy output load power operating conditions. Theturn-off circuit dynamically turns off the normally on switch as soon asthe snubber energy storage element has sufficient voltage to power thevoltage regulator and its downstream loads. As a result, the normally onswitch conductions losses are reduced improving the SMPS powerprocessing efficiency during all but the ultra-light load operatingconditions.

In accordance with an example embodiment, there is provided a combinedvoltage regulator and snubber circuit which generally has a voltageregulator device in parallel with the energy storage element of thesnubber circuit operatively connectable in series with a leakageinductance current path; the leakage inductance being part of a magneticcomponent utilized in a switch-mode power supply having an input voltagesource, controllable semiconductor switches, freewheeling semiconductorswitches, feedback controller, reactive energy storage components and aload; the voltage regulator generally providing constant or variablevoltage to the gate driver of the controllable semiconductor and/orfeedback controller.

In an example embodiment, there may be provided a switch-mode powersupply comprising: a transformer having a least one transformer inputand a load output, a converter cell, a low-dropout regulator, and anauxiliary winding. The converter cell may comprise: an input capacitor,a snubber circuit, the transformer input for a transformer connects inparallel with the snubber circuit, a switch driven by a gate driver andcontrolling the current through the transformer input, and a voltageregulator having an input and a regulated output. The snubber circuitmay comprise an energy storage device and a reverse-biased diodeconnected in series with the energy storage device. The regulated outputof the voltage regulator may connect to the voltage rails of the gatedriver. The input of the voltage regulator may connect in parallelacross the snubber circuit. The auxiliary winding on the at least onetransformer input may provide an auxiliary voltage to a low-dropoutregulator providing power to the input capacitor.

In another example embodiment, the switch-mode power supply may compriseone or more additional converter cells having the input of the voltageregulator of each additional converter cell connecting in parallel to aprior transformer input of a prior converter cell. A final convertercell may comprise the snubber circuit of the final converter cell havinga resistive element in parallel with an energy storage device of thefinal converter cell.

In any or all of the example embodiments, the energy storage device maycomprise a capacitor. A load may be connected to the load output of thetransformer. A feedback controller may monitor the load output of thetransformer in comparison to a reference voltage. The feedbackcontroller may comprise a subtraction block, a compensator, and amultiple-output pulse-width modulator (MPWM) generator controlling thegate driver of the converter cell. The voltage regulator may be selectedfrom: a switch-mode power supply, linear dropout regulator,switched-capacitor converter, shunt voltage regulator, series voltageregulator, or any combination thereof.

In any or all of the example embodiments, the voltage regulator maycomprise a voltage blocking device, connecting the input and regulatedoutput; a feedback control circuit, connecting the input port and acontrol port of the voltage blocking device; and a voltage referencecircuit, connecting the voltage blocking device and a relative zeropotential point. The voltage blocking device may comprise an NPN BITsemiconductor transistor. The feedback control circuit may be selectedfrom at least one of a resistor, a semiconductor transistor, a start-upvoltage regulator, and/or a combination thereof. The voltage referencecircuit may be a combination of a current independent and a currentdependent voltage reference. The current independent voltage referencemay be selected from at least one of a Zener diode, a forward biaseddiode, or a combination thereof. The current dependent voltage referencemay be selected from at least one of a resistor, a thermistor, and/or acombination thereof.

In accordance with another example embodiment, there is provided aswitch-mode power supply that may comprise a transformer having at leastone transformer input and a load output connected to a load, a pluralityof converter cells, a low-dropout regulator, and an auxiliary winding.The plurality of converter cells may be connected to each other andconfigured to receive a voltage input and provide a regulated output toone of the at least one transformer inputs. At least one of theplurality of converter cells may comprise an input capacitor across thevoltage input of the converter cell, a snubber circuit comprising anenergy storage device and a reverse-biased diode connected in serieswith the energy storage device, one of the transformer inputs connectedin parallel with the snubber circuit, a switch driven by a gate driverand controlling the current through the connected transformer input, anda voltage regulator having an input and a regulated output. Theregulated output of the voltage regulator may connect to the voltagerails of a gate driver. The input of the voltage regulator for at leastone converter cell may connect across the transformer input of a priorconverter cell. The input of the voltage regulator for the lastconverter cell may connect in parallel across the snubber circuit forthe last converter cell. The auxiliary winding on the at least onetransformer input may provide an auxiliary voltage to a low-dropoutregulator providing power to the input capacitor of at least one of theconverter cells.

In accordance with any or all of the example embodiments, the snubbercircuit of the first converter cell may comprise a resistive element inparallel with the energy storage device of the first converter cell. Theenergy storage device may comprise a capacitor. A load may be connectedto the load output of the transformer. A feedback controller may monitorthe connected load output of the transformer in comparison to areference voltage. The feedback controller may comprise a subtractionblock, a compensator, and a multiple-output pulse-width modulator (MPWM)generator controlling the gate driver of each converter cell.

According to yet another example embodiment, there is provided a methodfor a power efficiency of a switched-mode power supply having a voltageregulator. A source input power may be received from a transient energystorage element, an always energized energy storage element, or acombination thereof. The source input power may be directed from thealways energized energy storage element when the transient energystorage element is discharged and/or the source input power may bedirected from the transient energy storage element when the transientenergy storage element is available. A regulated voltage output may begenerated from the source input power suitable for use by a transformerproviding output power to a high-side electric load, a low-side electricload, and/or a combination thereof. The transient energy storage elementmay comprise a snubber energy element receiving a leakage inductanceenergy from the transformer. The always energized energy storage elementmay be a capacitor-divider.

According to any or all of the example embodiments, the switched-modepower supply may comprise at least one of a multi-winding flybackconverter or a stacked flyback cell converter.

Other features and variations of the example embodiments describedherein may become apparent to one of skill in the art on reading thepresent disclosure. The example embodiments herein are meant to beillustrative and not limiting.

BRIEF DESCRIPTION OF THE FIGURES

In the figures,

FIG. 1 is a schematic diagram of a multi-winding flyback converterutilizing capacitor-diode (CD) snubbers and two-port bi-directionalvoltage regulators connected to capacitive-divider input capacitors andsnubber energy storage elements in accordance with an exampleembodiment;

FIG. 2 is a schematic diagram of a stacked flyback converter utilizingCD snubbers and two-port bi-directional voltage regulators connected tocapacitive-divider input capacitors and snubber energy storage elementsin accordance with an example embodiment;

FIG. 3 is a two-port bi-directional voltage regulator circuit withnormally on depletion mode FET, resistive-divider based turn-off controlcircuit and series voltage regulator, in accordance with an exampleembodiment;

FIG. 4 is the two-port bi-directional voltage regulator circuit of FIG.3 whose mode of operation is highlighted for start-up and ultra-lightload conditions, where power to the series voltage regulator load isbeing provided from the input capacitive-divider energy storage element,in accordance with an example embodiment;

FIG. 5 is the two-port bi-directional voltage regulator circuit of FIG.3 whose mode of operation is highlighted for light-to-medium loadoperating conditions, where power to the series voltage regulator loadis being provided from the snubber energy storage element, in accordancewith an example embodiment;

FIG. 6 is the two-port bi-directional voltage regulator circuit of FIG.3 whose mode of operation is highlighted for heavy load operatingconditions, where power to the series voltage regulator is beingprovided from the snubber energy storage element and a portion is beingrecycled back to the input capacitive-divider energy storage element, inaccordance with an example embodiment;

FIG. 7 is a two-port bi-directional voltage regulator circuit withnormally on depletion mode FET, resistive-divider based turn-off controlcircuit and linear dropout regulator, in accordance with an exampleembodiment;

FIG. 8 is a two-port bi-directional voltage regulator circuit with ableeding resistor, energy recycling diode, and series voltage regulator,in accordance with an example embodiment;

FIG. 9 is a two-port bi-directional voltage regulator circuit with astart-up voltage regulator, energy recycling diode, and series voltageregulator, in accordance with an example embodiment;

FIG. 10 is a graph showing the evolution of the power processingefficiency as a function of output load current level for experimentalmulti-winding flyback converters from FIG. 1, in accordance with anexample embodiment; and

FIG. 11 is a depiction of a multi-winding flyback transformer windingstack-up, used in converters shown in FIG. 1, with an optimized trifilarprimary winding structure enabling reduced leakage inductance powerlosses.

These drawings depict exemplary embodiments for illustrative purposes,and variations, alternative configurations, alternative components, andmodifications may be made to these exemplary embodiments.

Like reference numerals may be used throughout the Figures to denotesimilar elements and features.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In accordance with example embodiments, there is provided a normally onswitch and associated turn-off circuit for further reducing theauxiliary power supply losses, having automatic turn-off capabilitiesduring light-to-heavy output load power operating conditions. Theturn-off circuit dynamically turns off the normally on switch as soon asthe snubber energy storage element has sufficient voltage to power thevoltage regulator and its downstream loads. As a result, the normally onswitch conductions losses are reduced improving the SMPS powerprocessing efficiency during all but the ultra-light load operatingconditions.

FIG. 1 is an example of a multi-winding flyback converter 102 forconverting alternating current (AC) to direct current (DC). Themulti-winding flyback converter 102 electrically connects a primary sideof a string of serially connected flyback converter cells 120 to asource input power 112 such as AC voltage source 112. Each of theprimary side flyback converter cells 120 contain a two-portbi-directional voltage regulator 160, gate driver 123, a CD snubbercircuit 121, primary-side transformer winding 150, and semiconductorswitch 125. The individual converter cell windings (e.g., primarywindings 150 a, 150 b, . . . , 150 k, secondary winding 150 x) arecoupled to the windings of other flyback converter cells 120 through asingle transformer core 152.

In addition, the bottom converter cell 120 voltage regulator 160receives transient energy from auxiliary voltage V_(aux) from anauxiliary winding 163. The auxiliary winding 163 comprises an auxiliarydiode D₂ and capacitor circuit C_(aux). A start-up LDO 164 is connectedto the first converter cell 120 (e.g., at the top-mostcapacitive-divider node) and is also connected to the auxiliary winding163. Also, the top converter cells 120 use the voltage CD snubber 121 ofneighboring converter cells 120 below. The snubber 121 capacitive energymay be recycled instead of dissipated via the regulated output voltagerail of the voltage regulator 160 and/or the bi-directional, normally-onswitch.

The secondary side port 300 of the multi-winding flyback converter 102is, in turn, connected into an output load 130 providing an outputvoltage V_(out). The output voltage V_(out) is sensed and isolated fromthe primary side via an isolator and compensator block 180 to produce acontrol signal v_(fb). The control signal v_(fb) is passed to a feedbackcontrol integrated circuit (IC) 170 that generates an SMPS switch on-offcontrol action with a duty-ratio relative to the analog value of thecontrol signal.

FIG. 2 is an example of a stacked flyback converter 100 using multipletwo-winding transformers 159 with one per flyback converter cell 120.The output rectification diodes D₁ to D_(k) 190 provide current inparallel to the output capacitor C_(out) and load 130. The top stackedflyback converter cell 120, in this example, uses aresistor-capacitor-diode (RCD) snubber circuit 121 b in order to clampthe semiconductor switch 125 peak voltage. Similar to the multi-windingflyback converter 102, the stacked flyback converter 100 also has thebottom converter cell 120 and voltage regulator 160 receives anauxiliary voltage V_(aux) from the auxiliary winding 163. The start-upLDO 164 is connected to the first converter cell 120 (e.g., at thetop-most capacitive-divider node) and is also connected to the auxiliarywinding 163.

FIG. 3 is an example of a two-port bi-directional voltage regulator 160that may be used in FIG. 1 or FIG. 2. The drain of the depletion moden-type FET 200 is connected via 208 to the higher potential node 208 a,b, . . . , k of the flyback converter cell 120 capacitive-divider energystorage C_(in). The source of the depletion mode n-type FET 200 isconnected at 209 to the higher potential node of the snubber capacitivestorage element. A series voltage regulator 211 and depletion moden-type FET (DFET) turn-off circuit is provided by a resistive divider,formed by R₁ 203 a and R₂ 203 b, a voltage reference circuit Z 202 (e.g.Zener diode), and voltage blocking device 201 (e.g. NPN BJT) and areconnected in parallel with the snubber capacitive energy-storageelement. The series voltage regulator has a decoupling capacitor 207connected in parallel with its output node.

The voltage regulator 160 may provide a path for power to flow from theinput capacitive-divider energy storage element 208 to the seriesvoltage regulator load, such as a gate driver 123 of FIGS. 1 and 2,during SMPS start-up or during periods when the snubber capacitiveenergy element 209 does not have sufficient energy. The current pathduring these periods is illustrated in FIG. 4 and is valid as long asthe gate-source voltage V_(gs) value is greater than the depletion-moden-type FET 200 threshold voltage value V_(th) (usually between −1V and−2.1V). In other embodiments, the current path may be determined byanother method such as the quality or noise of the transient energystorage element. The relationship between the turn-off voltage of thedepletion-mode n-type FET 200 and the rest of the voltage regulator 160components is given by,

$\begin{matrix}{v_{gs}^{off} = {v_{gs}^{th} = {{R_{1} \cdot I_{1}} = {R_{1} \cdot \frac{v_{Cs} - v_{z}}{R_{1} + R_{2}}}}}} & (1)\end{matrix}$

and may determine the turn-off point of the depletion-mode n-type FET200 to the instant when the snubber energy storage element has asufficiently large voltage value (e.g., V_(cs)>V_(z)). In such a way,the series voltage regulator may ensure reliable voltage regulation tothe gate driver or similar electronic loads during ultra-light loadoperating conditions while also minimizing the power consumption fromthe input capacitive-divider energy storage element 208. By selectingthe resistive-divider ratio and ensuring the worst-case snubbercapacitor voltage is greater than the minimum required by the loadconnected to the voltage regulator, the source input power is directedfrom the transient energy storage element when the transient energystorage element has available energy.

When the snubber energy element 209 has sufficient voltage to energizethe series voltage regulator and its electronic load, the depletion-moden-type FET 200 turns-off and the voltage regulator 160 power flow pathresemble that shown in FIG. 5. The stored leakage inductance 153 energyin the snubber energy element 209 is recycled via the well-regulatedseries voltage regulator, in the process reducing the SMPS power lossesand improving the power processing efficiency. The well-regulatedvoltage output may be suitable for use by a high-side (e.g., a floatingground) or low-side electric load (e.g., a load that has one nodeconnected to zero potential/common ground).

This embodiment allows for increased recycling of the leakage inductanceenergy during high output power load levels, when the snubber capacitiveenergy storage element 209 voltage is greater than the inputcapacitive-divider energy storage element voltage 208. By allowing theexcess energy, not being used by the series voltage regulator and itselectronic load, to flow into the input capacitive-divider energystorage element 208 via the body-diode of the depletion-mode n-type FET200 power processing efficiency can be further improved. The power flowpaths during this mode of operation are illustrated in FIG. 6.

FIG. 7 is another example of a two-port bi-directional voltage regulatorwhich is adapted to utilize a low-dropout linear regulator 204 insteadof a series voltage regulator 211 of FIG. 3. All other components aresimilar to the previously described examples above.

FIG. 8 is another example of a two-port bi-directional voltage regulatorwhich is adapted to utilize a resistor 210 and parallel diode 205instead of a depletion mode FET 200 of FIG. 3 for start-up powerdelivery and energy recycling. All other components are similar to thepreviously described examples above.

FIG. 9 is another example of a two-port bi-directional voltage regulatorwhich is adapted to utilize a start-up voltage regulator 206 and diode205 instead of a depletion mode FET 200 of FIG. 3 for start-up powerdelivery and energy recycling. All other components are similar to thepreviously described examples above.

Measured power processing efficiency for a 110Vrms to 5V experimentalmulti-winding flyback converter, using the depletion-mode normally ontwo-port voltage regulator 160 shown in FIG. 3 or FIG. 7, is presentedin FIG. 10. For comparison purposes the power processing efficiency oftwo additional multi-winding flyback converters, one using a bleedingresistor 210 and diode 205 circuit, shown in FIG. 8, and the other usinga start-up voltage regulator 206 and diode 206 circuit, shown in FIG. 9,instead of the depletion mode FET 200, are included in the comparison.The measured power processing efficiency at maximum power is best inclass (typical <85%), regardless of the proposed two-port voltageregulator 160 practical implementation.

FIG. 11 is a depiction of the multi-winding transformer windingstructure that may enable the reduction of power losses due to thetransformer leakage inductance energy in converters similar to thatshown in FIG. 1. The primary side winding 150 with the highest couplingto the other primary side windings 150, usually the middle primary-sidewinding 150 a, is connected to the top flyback converter cell 120. Sincethe top flyback converter cell 120 does not have a mechanism to recyclethe leakage inductance 153 energy, unlike the bottom flyback convertercells 120, the leakage inductance power losses may be minimized.

The example embodiments may provide an alternative method for thevoltage regulator to be powered during SMPS start-up or periods when theleakage inductance energy is insufficient to power the voltage regulatorload, through the capacitive-divider energy storage port and thenormally on switch path. In such a way, reliable operation of thevoltage regulator load may be ensured even under no load operatingconditions.

Although particular examples of the multi-winding flyback converter 102and stacked flyback converter 100, the example embodiments describedherein may be applied to converters, such as described in U.S. patentapplication Ser. No. 15/209,184 (Reference No. 51998-3001), hereinexpressly incorporated by reference in its entirety.

In the embodiments described herein, the energy storage devices, such ascapacitors and/or inductors, may be provided in the form of discretecircuit elements or may be integrated in an integrated circuit.

Although the embodiments described herein disclose a depletion-moden-type FET 200, other embodiments may comprise a gallium nitridesemiconductor switch and/or a bleeding resistor or similar device.

Although particular voltage regulators are described with reference tothe examples herein, other embodiments may comprise a shunt voltageregulator, a series voltage regulator, a miniature SMPS, a low-dropoutregulator, a switched-capacitor converter, and/or similar device. Theoutput of the voltage regulator may be connected to the load via afloating semiconductor switch gate driver, control circuit, or similardevice.

Variations may be made to some example embodiments, which may includecombinations and sub-combinations of any of the above. The variousembodiments presented above are merely examples and are in no way meantto limit the scope of this disclosure. Variations of the exampleembodiments described herein will be apparent to persons of ordinaryskill in the art, such variations being within the intended scope of thepresent disclosure. In particular, features from one or more of theabove-described embodiments may be selected to create alternativeembodiments comprised of a sub-combination of features which may not beexplicitly described above. In addition, features from one or more ofthe above-described embodiments may be selected and combined to createalternative embodiments comprised of a combination of features which maynot be explicitly described above. Features suitable for suchcombinations and sub-combinations would be readily apparent to personsskilled in the art upon review of the present disclosure as a whole. Thesubject matter described herein intends to cover and embrace allsuitable changes in technology.

What is claimed is:
 1. A switch-mode power supply comprising: atransformer having at least one primary winding, an auxiliary winding,and a load output; a converter cell, the converter cell comprising: aninput capacitor connected to a primary winding of the at least oneprimary windings at a first node, a snubber circuit comprising an energystorage device and a reverse-biased diode connected in series with theenergy storage device, the primary winding connected in parallel withthe snubber circuit by the first node and a second node, a switch drivenby a gate driver and controlling a current through the primary winding,and a voltage regulator having a first input, a second input, and aregulated output, the regulated output of the voltage regulatorconnected to voltage rails of the gate driver, the first input of thevoltage regulator connected to an energy storage device, the secondinput of the voltage regulator connected in parallel across the inputcapacitor; and one or more additional converter cells, wherein a firstinput of a voltage regulator of each additional converter cell connectsin parallel to an energy storage device of a snubber circuit of a priorconverter cell and a second input of the voltage regulator of eachadditional converter cell connects in parallel across an input capacitorof that additional converter cell.
 2. The switch-mode power supplyaccording to claim 1, further comprising another converter cell, whereina snubber circuit of the other converter cell comprises a resistiveelement in parallel with an energy storage device of the snubber circuitof the other converter cell.
 3. The switch-mode power supply accordingto claim 1, wherein the energy storage device comprises a capacitor. 4.The switch-mode power supply according to claim 1, further comprising aload connected to the load output of the transformer.
 5. The switch-modepower supply according to claim 4, further comprising a feedbackcontroller monitoring the load output of the transformer.
 6. Theswitch-mode power supply according to claim 5, the feedback controllercomprising a first output coupled to the gate driver of the convertercell, and a second output coupled to an additional gate driver of anadditional converter cell.
 7. The switch-mode power supply according toclaim 1, wherein the voltage regulator comprises one or more of aswitch-mode power supply, a linear dropout regulator, aswitched-capacitor converter, a shunt voltage regulator, or a seriesvoltage regulator.
 8. The switch-mode power supply according to claim 1,wherein the voltage regulator comprises: a voltage blocking device,connecting the second input and the regulated output; a feedback controlcircuit, connecting an input port and a control port of the voltageblocking device; and a voltage reference circuit, connecting the voltageblocking device and a relative zero potential point.
 9. The switch-modepower supply according to claim 8, wherein: the voltage blocking devicecomprises an NPN BJT semiconductor transistor; the feedback controlcircuit comprises one or more of a resistor, a semiconductor transistor,and a start-up voltage regulator; and the voltage reference circuitcomprises a current independent voltage reference and a currentdependent voltage reference.
 10. The switch-mode power supply accordingto claim 9, wherein: the current independent voltage reference comprisesone or more of a Zener diode, or a forward biased diode; and the currentdependent voltage reference comprises a resistor.